The first shift of Santa trackers started taking calls early Monday, telling children — and some adults — when Santa is due at their house. The last shift won’t end until nearly 24 hours later.

The volunteers are working from Peterson Air Force Base in Colorado Springs, home of the North American Aerospace Defense Command. About seven hours into the day, they’d received more than 24,000 calls.

Some kids wanted to know more than where Santa was and when he would be at their house.

“How old is Santa?” one caller asked. The answer to that one is in the FAQs that NORAD hands out to volunteers: “It’s hard to know for sure, but NORAD intelligence indicates Santa is at least 16 centuries old.”

Other questions require the volunteers to think fast:

“How do reindeer fly?”

“How many elves does Santa have?”

“Does Santa leave presents for dogs?”

One little boy from Missouri phoned in to ask what time Santa delivered toys to heaven, said volunteer Jennifer Eckels, who took the call. The boy’s mother got on the line to explain that his sister had died this year.

“I think Santa headed there first,” Eckels told him.

NORAD suggests its volunteers tell callers that Santa won’t drop off the presents until all the kids in the home are asleep. The response depends on the caller’s age.

“Ohhhhhhh,” said an 8-year-old from Illinois, as if trying to digest a brand-new fact.

“Thank you so much for that information,” said a grateful mom from Michigan.

NORAD, a joint U.S.-Canada command responsible for protecting the skies over both nations, says its Santa-tracking rite was born of a humble typo in a newspaper ad in 1955.

The ad in a Colorado Springs newspaper invited children to call Santa but inadvertently listed the phone number for the Continental Air Defense Command, NORAD’s predecessor, also based in Colorado Springs.

CONAD officers played along, and word spread that this Cold War military command charged with guarding the U.S. against an attack by the Soviet Union was also telling kids where Santa was.

Since then, NORAD Tracks Santa has gone global, progressing through bulletins on AM radios and black-and-white TVs to updates on Facebook, Twitter and smartphone apps.

Last year, volunteers answered almost 102,000 calls, nearly 25 percent more than the previous year. They also answered more than 7,700 emails (noradtrackssanta@outlook.com).

The NORAD Tracks Santa website attracted 18.9 million unique visitors from 220 countries and territories during December 2011.

This year, the program has more than 1 million likes on Facebook and more than 114,000 followers on Twitter days before the tracking operation got under way.